In previous hitch head or fifth wheel constructions, it has been common to provide a pair of rotatable jaws which in closed position hold in place the kingpin of a highway trailer, and which are biased to assume an open position allowing removal of the kingpin by a pair of torsion springs attached respectively to each of the jaws. The torsion springs tend to prevent the jaws from moving to the closed position without the presence of a kingpin to force the motion.
However, it has been found that in service the torsion springs occasionally become inoperative or break, requiring that the hitch be taken out of revenue service and be dismantled to replace the broken or inoperative torsion springs.
If the torsion springs are not replaced and the hitch remains in service, there is a danger that one jaw will return to closed position and prevent entry of the kingpin.